I usually do about 250ml black coffee, 500ml water, and two slices toast with peanut butter + banana about 3 hours before, then a caffeinated Gu gel immediately prior to start and again at 8km/16km/24km/32km. Try to drink a bit of water of whatever electrolyte mix they are giving out at most aid stations or carry a handheld 400ml bottle to sip on throughout if I think the aid station are going to be chaos.
-What are you eating/drinking before and during a marathon? How much and when?
-Is Maruten or tailwind actually better than Gus Gatorade etc.?
-How much fluid do most consume during race in moderate spring/fall conditions?
-Potassium/sodium pills?
-Nitrates /beet juice?